The present invention relates to a capacity control apparatus for use in co-operation with compressor in a refrigerating cycle of an automobile air-conditioner or the like.
As the compressor in the refrigerating cycle of an automobile air-conditioning system directly is driven from the engine via a belt, the individual speed of the compressor cannot be controlled. In order to obtain proper refrigerating ability without limitation by engine speed, a compressor is used, the capacity of which (the amount of discharged refrigerant) can be varied independent from the compressor speed. Conventional compressors are of the inclined board type, rotary type or a scroll type, or of other types. An inclined board type compressor has a crank chamber serving as a pressure control room for controlling the capacity. The interior pressure of said pressure control chamber affects the initial capacity of the compressor. The capacity is changed by automatically controlling a control pressure (Pc) in the crank chamber corresponding to variations of an inhalation pressure (Ps) of the compressor. In the capacity control apparatus a pressure control valve serves to open or close a flow passage between the crank chamber (pressure control chamber) and an inhalation chamber of the compressor. Said valve opens and closes corresponding to variations of the inhalation pressure. In closing direction the pressure of the ambient air is active in combination with an energisation force adjusted by a solenoid. Said forces are transmitted in opening direction via a diaphragm onto which also the inhalation pressure is acting. Said pressure control valve opens and closes and thus varies the level of the pressure in the crank chamber. A chamber within the pressure control valve defined between a valve seat and said diaphragm communicates with said pressure control chamber. The other side of said valve seat communicates with the inhalation chamber. Control pressure (Pc) in said crank chamber should not affect the balance of said pressure control valve in order to control the capacity correctly. For that reason the pressure effective area of said diaphragm has to be dined much larger than the pressure effective area within said valve seat. If the pressure effective area of said diaphragm is large, the solenoid adjusting the energisation force for the pressure control valve also has to be large and heavy resulting in an undesirable large size of the apparatus and high costs. If the pressure effective area within said valve seat is reduced, the throttling effect of the refrigerant flow through said valve seat is significant, resulting in an undesirably delayed response behavior of the capacity control apparatus.
It is an object of the invention to provide a capacity control apparatus having small size which can be produced with fair costs.
Due to at least essentially equal pressure effective sizes of the areas on the diaphragm and inside the valve seat the control pressure (Pc) in the pressure control chamber or crank chamber does not affect the balance of opening and closing strokes in the pressure control valve chamber. Said valve seat communicates outside said chamber with the inhalation room. A small sized pressure effective area of the diaphragm suffices for a proper control function. As a consequence, said small sized pressure effective area of the diaphragm allows to use a small sized and cheap solenoid. Since there is no need to use a small sized pressure effective area for said valve seat but instead the same pressure effective area than the pressure effective area of said diaphragm can be used. As a result, the response behavior of capacity control is not delayed during e.g. an opening stroke of the pressure control valve. The control behavior of the pressure control valve is stable. It is not necessary to restrict the flow between the inhalation chamber and the crank chamber by a small cross-section in the passage at the valve seat.